Wind turbines are attracting attention as environmentally-friendly power generation equipment. In a wind turbine, blades and a nacelle are installed at a high altitude (for example, several tens of meters from the ground) on a support, wherein the blades convert a wind force into a rotational force, and the nacelle houses converters (a gearbox and a power generator) for converting the rotational force into electric power. The nacelle is rotatably supported on the support, and is configured to rotate in accordance with a wind direction.
In such a wind turbine, various types of condition monitoring is performed. For example, an abnormality predicting apparatus using an acceleration sensor, which is applicable to condition monitoring of, for example, a bearing for a main shaft that transmits the rotational force from the blades, or a bearing provided in the gearbox, is known (see, for example, PTD 1).
Moreover, Japanese Patent Laying-Open No. 2011-185632 (PTD 2) discloses an abnormality detecting apparatus that accurately detects an abnormality in a bearing provided in the blades of a wind turbine, based on a change in a natural frequency obtained through analysis of the frequency of a vibration signal detected using a vibration sensor (see PTD 2).
On the other hand, for condition monitoring of a non-rotary part (typically a support (tower)) of a wind turbine, abnormality detection is currently performed through regular visual checks or hammering checks.